Hydraulic remote indicating apparatus



Sept. l2, 1944. G. c. R. BIRCH HYDRAULIC REMOTE INDICATING APPARATUSFiled June 12, 1942 J/ Hl 2,358,047 O F F l C E HYDRAULIC REMOTEINDICATIN G APPARATUS Gmc ciu-imm am auch, amas Park, Eng;

land, 4assigner to B. B. Patents Limited, London, England, a company o!Great Britain Application June 12, 1942, Serial No. 446,826 Gre BtltllnJuly 16, '1941 comme (01..'13-310) walled metal capillary'tube B, and asecondv simi- This invention relates to hydraulic remote indicatingapparatus of the kind in which an indicator element is controlled by abellows or like expansion chamber connected through a Pipe to a deviceresponsive to the quantity to be indicated, compensation for temperatureexpansion or contraction of the liquid in the pipe and bellows beingaiorded by a second similar bellows or like expansion chamber connectedto a second pipe adjacent to the first pipe. Although not limitedthereto, the invention is more -particularly concerned with apparatus ofthis kind for indicating temperature, the device at the remote end ofthe pipe connected to the operating chamvber consisting of aliquid-filled bulb exposed to the temperature to be measured.

In known apparatus of this kind the two bellows are arranged to expandtoward one another, in opposite directions along parallel but oiIsetaxes, and are connected to the ends of a iloating lever Whose mid-pointoperates the indicator element. Thus with Aambient temperature changesequal movements of the two bellows will cause the lever to swing aboutits mid-point without moving the indicator element, whilst a change inthe bulb temperature or other quantity to be measured will affect onlythe operating bellows, the floating lever swinging about its point ofconnection to the compensating bellows and thus operating the indicatorelement.

Such an arrangementl however introduces slight inaccuracies in theresultant indication owing to the fact that at different ambienttemperatures the mid-point of the floating lever swings about differentcentres. If the oating lever were -very long, so that its angularmovement throughout the whole range of ambient temperature changes weresmall, these inaccuracies would be negligible. In practice, however, itis inconvenient to employ a long lever, and the present invention hasfor its object to provide an improved arrangement of hydraulic remoteindieating apparatusof the above-mentioned kind, wherein suchinaccuracies are avoided without the necessity for the use of a longfloating lever. The arrangement according to the invention also has theadvantage of providing a relatively robust indicating apparatus ofsimple construction not requiring any very high degree of accuracy inthe manufacture of its parts or in the balancing of the operating andcompensating hydraulic sys- A tems with one another.

Further objects of the invention will be apparlar capillary tube Cextends along the whole length of the ilrst and is sealed at its end C1adjacent to the connection Bl of the rst tube B to the bulb A.

'I'he apparatus at the indicating end is vmounted l on a suitable baseD, which for convenience of description will be assumed to consist oi adat board mounted vertically i although it may be arranged in` otherways. 4The two capillary tubes B C are connected at their ends tojunction pieces Bz C2 ilxed to the bottom oi' the board D, and from oneof these junction pieces C2 (namely that connected to the compensatingcapillary tube C) a short pipe C3 leads to the upper end cover plateliil of a vertically mounted metal bellows E, this cover plate beingsupported on a bracket D1 ilxed to the board'D near one side edgethereof.

The lower end cover plate En of this compensating bellows E carries anarm lils pivoted to one end of a short lever arm F having a horizontalslot F1 which can slide past a pivot pin F on a bracket U xed to thebase board. This lever arm F can be clamped by a clamping screw F3 inany desired position of adjustment to a second lever arm F4 pivotedabout the pin F, and this second lever arm F* carries a segmentaltoothed rack F5 centred about the pin.

This rack F5 engages with a similar rack Ci on a lever arm GA which ispivoted about another iixed pin Gf2 and to which a slotted lever arm Gcan be clamped in any position of adjustment, this slotted lever arm Gbeing connected to the lower end cover plate H2 of the operating bellowsH. The two lever and rack mechanisms are similar to one another and actto ensure that, when they are similarly adjusted, any movement of thelower end of one bellows must be accompanied by an exactly similarmovement of the lower end of the other bellows.

Theupper end cover plate H1 of the operating bellows H is not fixed butis connected to the indicator pointer J, and since both ends of thisbellows are movable, it is necessary to employ a 'slightly iiexibleconnection from the junction piece B2 connected to the operatingcapillary tube B. 'I'his is achieved by the use of a coll B3 of iinecapillary tubing, the internal diameter of which is considerably smallerthan that of the short pipe C'3 from the other junction piece Cato/compensate for the difference in length between them, `so that theyshall both contain approximately the same volume of liquid.

'I'he upper end cover plate H1 of this bellows H is connected by avertical link J1 (of adjustable length) whose uppen end 'can be clampedin any chosen positionf Iin. a horizontal slot Jz in one arm of atwo-armed lever J3. The other arm oi' this lever J3 carries a segmentalrack J4 engaging with a small pinion Js directly mounted on theindicator pointer shaft. The provision of the slot J in the'lever armpermits adjustment to suit any desired ratio between the bellowsmovement and the pointer movement, so that the same apparatus can beemployed for various ranges o! temperature indication, withappropriately calibrated scales. In order to prevent backlash in themovement a light spiral spring J is provided onthe pointer shaft, and amore powerful helical` spring J7 acts on the horizontally slotted leverarm J3 to give a smooth and steady pointer movement. -The range oftemperature which can be indicated is limited only by such factors asthe boiling and freezing points o! the liquid employed and the lengthand expansibility of the bellows,'and it will readily b e appreciatedthat, with suitable adjustment of the horizontally slotted arm J, a goodwide-open substantially even scale can be obtained for any desiredtemperature range for which liquids are available, as may -be requiredfor the particular purpose for which the thermometer is to be used.

In order to reduce the total quantity oi liquid in each bellows H or Eone of the cover plates H or E2 may be cup shaped, so that when thebellows is collapsed to its minimum size the base oi' this cup comesnearly into contact with the other cover plate H1 or E, the .bellowsthus still being capable of its full range of movement.

Assuming that the two hydraulic systems, each comprising capillary tubeand bellows, are exactly similar to one another and the two levermechanisms below the bellows are similarly adjusted, it will be clearthat an ambient temperature increase will cause the compensating bellowsE to expand downwards, the mechanism causing the lower end of theoperating bellows H to move downwards by the same amount. Since howeverthe expansions of both bellows will be equal, the upper end oi' theoperating bellows H will remain stationary and the pointer J will remainunaiected. 'I'his will of course apply equally to a decrease vin ambienttemperature, and also to local temperature changes which affect only apart of the two systems.

If however the two hydraulic systems are not quite similar, themovements of the two bellows will be slightly different, but since theexpansion law is a linear law, the movements will be proportionalto oneanother and can be exactly corrected by appropriate adjustment of thelever mechanisms.

'I 'he` arrangement also affords compensation for any diiIerence ofstatic head being the ends of the apparatus, since this will affect thetwo systems equally and will therefore have no eiect except to alter thepositions of the lower ends of the two bellows.

A change in the temperature to be measured on the other hand will causeexpansion only of the operating bellows H and since the lower end oi'such bellows will be held stationary by the compensating bellows E, itsupper end will move through the appropriate distance and will operatethe pointer J.

It will be appreciated that the foregoing arrangement has been describedby way of example only and may be modified in variousways within thescope of the invention, and that the irvention may be applied topurposes other than temperature. measurement.

What I claim as my invention and desire to secure by Letters Patent is:

i. Hydraulic remote indicating apparatus comprising in combination aclosed hydraulic system consisting of a device responsivev to thequantity to be indicated, a longitudinally expansible chamber and a pipeconnecting the device and the chamber, a second closed hydraulic systemconsisting of a second longitudinally expansible chamber disposed sideby side with the iirst and a second pipe extending from such chamberclosely adjacent to the first pipe, an indicator element, means foroperatively connecting such element to one end oi one chamber, means forfixing the corresponding end of the other chamber, and mechanisminterconnecting the other ends of said cham-bers for constraining one tofollow the movement o'! the other in the same direction at proportionalspeed.

2. Hydraulic remote indicating apparatus as claimed in claim 1, inwhich` the interconnecting device incorporates means for varying therelative position of associated parts oi said interconnecting mechanismto adjust the transmission ratio thereof to vary the ratio between thespeeds of the two chamber ends.

3. Hydraulic remote indicating apparatus claimed in claim l, in whichthe interconnecting device comprises a pair of pivoted leversrespectively connected to the chamber ends, and a pair oi intermeshingsegmental racks respectively carried -by the two levers.

4. Hydraulic remote indicating apparatus as claimed in claim 1, in whichthe interconnecting device comprises a pair of pivoted levers o!adjustable lever ratio respectively connected to the chamber ends, and apair-of intermeshing segmental racks respectively carried by the twolevers. f

5. Hydraulic remote indicating apparatus comprising in combination aclosed hydraulic system consisting oi' a device responsive to thequantity to be indicated, an expansible bellows and a pipe connectingthe device and the bellows, an indicator element, means for operativelyconnecting the forward end of the said bellows to such element, meansfor compensating for ambient temperature variations comprising a secondbellows similar to the ilrst and disposed side by side therewith withits forward end fixed, a second pipe extending closely adjacent to theiirst pipe and constituting with the second bellows a second closedhydraulic system, mechanism interconnecting the other ends of the twochambers for constraining their movements relative to one anotherwhereby the two chamber ends can only move in the same direction at thesame proportional speeds, and means associated with said mechanism forvarying the relative positions of associated parts thereof to adjust thetransmission ratio to accommodate any difierences between the quantitiesof liquid in the two hydraulic systems whereby the forward ,end of thefirst bellows remains unaffected by ambient temperature changes, andmoves only in response to changes in the quantity to be indicated.

6. Hydraulic remote .indicating apparatus as claimed in claim 5, inwhich theadjustable interconnecting device comprises a pair of similarpivoted levers oi' adiustable lever ratio respectively connected to therearward ends of the two bellows, and a pair of similar intermeshingsegmental racks respectively carried by the two levers.

GEORGE CHRISTIAN ROSS BIRCH.

